<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>
   <script>
       var a = prompt("请输入您的姓名");
       if(a == "张三"){
           alert("欢迎你张三");
       }
       else if(a == "李四"){
           alert("欢迎你李四");
       }
       else{
           alert("欢迎你帅哥美女");
       }
   </script>
</body>
</html>